The Microsurgical Core (Core B) plays a central role in the strategies for achieving the specific objectives of this Program. All projects depend on the technical expertise of the Core B facility and this technical expertise is the foundation for the Program. As this Program was originally organized, it became obvious to all the investigators that in order for them to pursue studies in the area of renal transplantation, each would have to train one or two transplant technicians, equip surgical stations, and maintain populations of animals independently. By combining efforts in a Program Project that provided a core laboratory for maintaining animals and performing transplant surgery, a tremendous amount of money and effort could be saved. The numerous ongoing collaborations, the enthusiasm for the pursuit of studies in the area of transplantation and the legitimate need for the development of a Core facility provided the impetus for the original development of this Program Project. These circumstances have persisted and in fact the enthusiasm and demand for the Core services have steadily increased. The primary role of the Microsurgical Core facility continues to be providing mouse transplants to Project investigators. For the current proposal, the core will provide both kidney and heart transplants. This Core also provides capabilities for measuring renal transplant function as specified within the individual proposals. The techniques for transplantation and the experimental utilization of transplanted animals is described in detail in the individual Project proposals.